Some examples of stepless gear ratio variators in which motion is transmitted by friction already exist in the market. Operation of said variators is obtained in two ways: either by increasing the number of members involved in the transfer of torque or by increasing the single surface in contact with respect to that guaranteed by punctiform contact.
However, said solutions are particularly complicated and bulky from a constructional point of view and also entail considerable production costs.
In a further solution of embodiment, transmission of motion between the driving member and the driven member takes place through the friction of a pair of elements with contact surfaces both convex or also only one convex and the other concave, preferably coated with suitable composite materials (ceramic or of other type) and translating simultaneously along the respective incident axes of rotation, in order to remain constantly in contact. Examples of this technical solution are described in the international patent application WO2008/102167 by the English company TOROTRAK DEV LTD or in the European patent application n. 1026424 by the Japanese company Isuzu Motors LTD. However, it should be noted that also the technical solutions described in these patent documents are somewhat complicated from the point of view of production, as in order to maintain the elements permanently in contact, it is necessary to act on both by means of a hydraulic pump which requires a specific circuit.